Alpha rendering with White background
Does it help if you switch the shading of the 3d view to GLSL? You can switch between "Multitexture" and "GLSL" in the properties panel (open with N key in the 3d view), under the "shading" group. Material alpha should be 0, and texture alpha influence > 0 (texture transparency shows transparent in the material) or &lt;0 (the inverse of the texture transparency   shows transparent in the material) 

See this example: